1. Field of the Invention
The present invention relates to a lens device, and more particularly, to a lens device provided in a portable image taking apparatus.
2. Description of the Related Art
A lens device is provided with a plurality of taking lenses that move in the direction of the optical axis, such as a focus lens and a zoom lens (see, for example, JP-A-2005-114811). In such moving-type taking lenses, normally, the holding frame thereof is engaged with two guide bars, one guide bar acts as a main guide in the direction of the optical axis, and the other guide bar acts as a detent for the lens holding frame. That is, the lens holding frame is provided with: a guide portion slidably engaged with the guide bar as the main guide; and a detent portion engaged with the guide bar as the detent to restrict the movement in the rotation direction. The guide portion has a predetermined length in the axial direction in order to prevent the lens holding frame from rattling, and by the guide portion sliding on the guide bar, the lens holding frame is moved in the direction of the optical axis.
When a plurality of moving-type taking lenses are provided, the guide bars are made common to the lens holding frames of the taking lenses. For example, in a lens device having a zoom lens and a focus lens, the guide portion of the zoom lens side and the guide portion of the focus lens side are engaged with the guide bar as the main guide, and the detent portion of the zoom lens side and the detent portion of the focus lens side are engaged with the guide bar as the detent. Thereby, common guide bars can be used among a plurality of taking lenses, so that the number of parts can be reduced to thereby reduce cost.
However, when the guide bars are made common to a plurality of taking lenses, the size of the lens device cannot be reduced. That is, since it is necessary for the guide portions to have a predetermined length in the axial direction, if a plurality of guide portions are engaged with one guide bar, a large space is required in the axial direction, so that the size of the lens device is increased in the axial direction.
Therefore, a method is considered in which a plurality of guide portions are disposed so as to be divided between two guide bars. For example, the guide portion of the zoom lens side is engaged with a first guide bar so as to act as the main guide of the zoom lens size, whereas the guide portion of the focus lens side is engaged with a second guide bar to act as the main guide of the focus lens size. In that case, the detent portion of the focus lens side is engaged with the first guide bar, and the detent portion of the zoom lens side is engaged with the second guide bar. Thereby, the two guide portions are disposed so as to be divided between the two guide bars, so that the size of the lens device can be reduced.
However, in the above-described case, since the two guide bars each act as a main guide, it is necessary to attach the two guide bars so as to be parallel to the optical axis with high accuracy, and the assembly work requires a great deal of labor.
Moreover, it is desirable that the guide bars be parts selected according to the processing accuracy of the guide holes of the guide bars or selected for each rod of the guide bars or the guide portions. However, when both of the two guide bars are the main guides, in order to maintain high parallelism with the optical axis, it is necessary to change the design every time the guide bars are changed, so that the guide bars cannot be selected parts.
As a method for solving such a problem, a method is considered in which a plurality of attachment holes larger than one ends of the guide bars are provided on the lens barrel body, the one ends of the guide bars are inserted in the attachment holes and pressing members are press-fitted in the clearances between the one ends and the attachment holes. In that case, by pressing the one ends of all the guide bars in the same direction by the pressing members, all the guide bars can be fitted in the lens device with high parallelism. Moreover, even guide bars having different diameters can be fixed to the lens barrel body, so that the guide bars can be selected parts.
However, in such a method, a problem occurs in that the pressing member readily falls off from the lens barrel body. Since the guide bar moves or falls off if the pressing member falls off, the guide bar cannot be used as the main guide.